Film coalesced latex impregnated paper and process therefor



K. ISAACS 3,483 025 FILM COALESCED LATEX IMPREGNATED PAPER AND PROCESSTHEREFOR Dec. 9, 1969 Filed July 21, 1966' PHILIP K. ISAAOS BY 7W 7ATTORNEY United States Patent U.S. Cl. 117-155 5 Claims ABSTRACT OF THEDISCLOSURE The invention disclosed is directed to an impregnated papercomprising a cellulosic pulp paper impregnated with coalesced syntheticpolymer latex solids With substantially all of the solids beingcoalesced on the surface of fibers in the paper so that the interior ofthe fibers are substantially free of latex solids. The paper isimpregnated in a process which comprises contacting a synthetic polymerlatex with an organic cation/free base organic anion exchange resin andthereafter applying the latex to a cellulosic pulp paper. In a preferredembodiment of the present invention, the latex contains from about 5% toabout 70% synthetic polymer and more preferably from about 15% to about50%.

The present invention relates to a novel and useful product and aprocess for preparing the product. More particularly, it relates to animpregnated paper and a process for impregnation.

It is known in the art that various latex impregnated papers may be usedin the manufacture of pressure sensitive tapes, shoe insoles, artificialleather bases and the like". In the preparation of the latex for paperimpregnation, two distinct systems are utilized. The first systemutiilzes a monomer, water, soap and an initiator which are mixed withheat and pressure. The second system utilizes the polymer, water, aquite large quantity of surfactant and energy which is generallyimparted in the form of mixing to disperse the particles. The latexresultingfrom each of these systems, when applied to a paper, usuallyresults in a bridging of polymer strings between thepaper fibers andsome actual penetration of the polymer into the fibers. The bridgingresults in a waste of polymer since the bridges add little, if any, tothe strength of the paper. The penetration of the polymer into thefibers also results in a loss of polymer since it actually detracts fromthe strength of the fibers it has penetrated. In addition, the surfaceactive agent used impair the physical properties of the paper and theresulting tapes are generally not suitable for electrical Work since thesurfactant increases the conductivity in the finished product. Quiteobviously, if a system could be developed which did not utilize asurface active agent and resulted in the fiber being uniformly coatedwith substantially no bridging or penetration, it would receivewidespread acceptance in the art.

It is an object of the present invention to provide a process forpreparing an improved latex. A further object is to provide animpregnated cellulosic pulp paper. A still further object is to providea more uniformly impregnated cellulosic pulp paper. Other objects willbecome apparent as the description of the invention proceeds.

These objects are accomplished by the present invention which provides aprocess for impregnating paper which comprises contacting a syntheticpolymer latex with an organic cation/free base organic anion exchangeresin and thereafter applying the latex to a cellulosic pulp paper.

In a preferred embodiment of the present invention,

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the latex contains from about 5% to about 70% synthetic polymer and morepreferably from about 15% to about 50%.

The present invention also provides an impregnated paper comprising acellulosic pulp paper impregnated with a coalesced synthetic polymerlatex solids with substantially all of the said solids being coalescedon the surface of the fibers in the paper so that the interior of thefibers are substantially free of said latex solids.

In a preferred embodiment of the present invention the impregnated papercontains at least about 20% synthetic polymer latex solids and morepreferably from 30 to In a still more preferred embodiment, theimpregnated paper contains from 40 to 60% synthetic polymer latexsolids.

The term latex is used in its conventional sense to mean a dispersion ofsolid synthetic polymer particles in water which is capable of forming afilm from the dispersion. The synthetic polymers which can be utilizedin the latex includes, without limitation, polymers and copolymers ofbutadiene, isoprene, chloroprene, acrylates, vinyl halides, vinyl estersand the like. Specific examples include the homopolymers polyethylacrylate, plasticized polyvinyl chloride and the copolymersstyrene-butadiene (40%60%) and styrene-acrylonitrile-butadiene-acrylicacid (35 %14%50%1% Other polymers are likewise suitable.

The expression organic cation/free base organic anion exchange resin isused to signify all the conventional organic resins which are utilizedfor the removal of anions and cations from solutions. The solution maybe passed sequentially through the cation exchange resin and then theanion exchange resin (or vice versa) or the resins may be utilized as amixed bed. Preferably, the anion exchange resin is a strong base resinsince a longer contact time is required with the weaker resins. In manyinstances, the anion exchange resin is furnished in the form of thechloride since it is more stable in this form. In such cases, thechloride should be changed to the free base before being used as thefree base does not add ions to the solution. Anion and cation exchangeresins are well known in the art and are described in numerouspublications, books and patents. A partial list of suitable organicanions and cations resins is given in the Encyclopedia of ChemicalTechnology (1952), volume 8, page 13. Other organic resins are alsosuitable and may be found in any standard textbook on ion exchange.

The terminology cellulosic pulp paper is used to mean any conventionalpaper such as that made from Wood pulp, cotton linters and the like. Italso includes paper which contains some synthetic filaments asreinforcement. The term coalesce merely signifies that the polymer hasbeen heated sufficiently so as to fuse the particles together.

The invention will now be described by reference to the drawings. In thedrawings:

FIGURE 1 is an artists conception of an enlarged cross sectional view ofa sheet of impregnated paper produced in accordance with the prior art;and

FIGURE 2 is an artists conception of an enlarged cross sectional view ofa sheet of impregnated paper produced in accordance with the presentinvention.

In FIGURE 1 the paper fibers 1 have been penetrated by the polymer 2 andstrings of the polymer 3 bridge the individual filaments. The figuredemonstrates that the prior art procedures result in a waste of polymerby the bridges being formed and by the polymer penetrating into thefibers.

In FIGURE 2 the paper fibers 4 are substantially uniformly coated withthe polymer 5. The figure demonstrates that very little polymer isWasted when the impregnated paper is made in accordance with the presentinvention since the polymer is quite uniformly coated onto thefilaments.

The following examples are given to illustrate the invention and are notintended to limit it in any manner. All

4 tore. The tear strength is reported in grams/mil. A fixture comprisinga triangular (904545) plate, attached by a pivot (at the 90 angle) to aA inch rod, is set into the hole in the paper, rod first. The apex ofthe triangle just touches the paper at the start of the test.

parts are given in parts by weight unless otherwise ex- The electricalresistance tests are carried out using pressed. the ASTM-Dl000 testprocedure.

In the following examples, the tests are carried out as follows. EXAMPLE1 The percent total solids in the latex is determined by To 1000 gramsof a latex containing 50% of solids accurately Weighing a sample of thelatex: drylhg h (40% styrene-60% butadiene copolymer) is mixed withsample to constant weight and reweighing. The total solids 200 grams ofa mixed bed ion exchange resin and 00 a n Calculated fIOIIl thefollowing formula: grams of water. The cation portion of the mixed bedis Dry weight a styrene/divinyl benzene sulfonic acid resin. The anion m100 perceht total so Ids 5 portion of the bed is a quaternary base of astyrene/ divinyl benzene copolymer having a tetramethylamino- Tensileproperties, i.e., tensile strength at failure, permethyl group attachedto the benzene rings (free base cent elongation at failure and 1 percenttensile modulus form of resin) The resin is described in I. A. Kitchenerare measured in accord with ASTMD41264T. The Exchanoe' Resin Methuen andLtd London copolymer latex is dried in film form (3 mils thick), cut(1957), mixture is Stirred at O for 3 to /4" sample strips, placed inthe aws, (2" ap of hours and then filtered to remove the resin. Ashcontent tensile strength tester (Instron, Model TT, available from Shownthat Over 95% of the ions are removed The final Ihstron Engineering hQuincy Mas?) and Separated at solids content is 35 to 40%. A standardsize sheet (8 /2 a F of Per mlhute and strain fa of 50% Per inch by 11inches) of cotton linters paper (12 mils thick) mmute at Cgand 9 Telahvehum1d1ty- 25 is impregnated with the latex by dipping the base into Thedclamination resistance is measured by preparing the latex to give animpregnatfid paper having 40% Poly test specimens which are cut to alength of approximately mer solids (dry weight) The Sheet is dried atroom 4 /2 inches in machine direction and a width of approxitfimpemwmmately 2 inches in the cross direction of the paper. The. When theimpregnated sheet is examined under a high test specimens areconditioned 48 hours at 23 C. and 50% powemd microscope it can be Seenthat the fib r h relative hUIhidhX-AS'iHChIOhg Strip of'rug binding Pbeen quite uniformly coated with the latex solids with Placed on eachslde of the Paper Specimen so that the substantial absence of anystrings or bridges conextends beyond the ends of the paper. The pecimen18 meeting the fibers. By taking /2 of the paper sheet before thenplaced011 h bottom platen of a Press 50 that 1 drying, the latex on theexterior of the sheet can be PFOXImateIY lheh of the p eXtehdS beyondthe ehd removed by washing with water leaving only that latex of the pThe Specimens are Pressed 30 seconds at which has penetrated into thefibers. A comparison of the 2750 at Pressure of Pounds P Square inch onweight of the washed dried sheet with the weight of the ihe binding PThe Specimens Cooled to room original sheet, shows that substantially nolatex has penel The Specimens are Cut in strips aPPTOXlIIIateIY 1 tratedinto the fibers. In contrast, when a control latex is inch Wide- The twoends of the rug binding p are Pulled carried through the same procedurewithout the treatment, apart into tWO pp y equal P The ends of the agreat deal of bridging takes place between the fibers binding p are Pinto the l of the Instfoh Tensile of the paper. Also, by the removal ofthe latex solids from tester after the first inch of Separfioh, theaverage the sheet, it can be determined that about 15% of the forcerequired to Separate the P p is recorded at a CTOSS- latex solids haspenetrated the interior of the fibers. head speed to 10 inches/min. Thedelamination resistance of the paper is reported in pounds based on theaverage EXAMPLES 2 5 Values of 3 specimens- The procedure of Example 1is repeated utilizing a The fold endurance is tested in accordance tothe commercial mixed bed anion and cation exchange resin. 7 testingProcedure. The commercial resin wherein the cation exchange resin Theteal" Strength is tested y the following Procedure: consists of asulfonated copolymer of styrene and divinyl Samples are Cut into PieceS1 inch y 41/2 inch and Condibenzene combined with an anion exchangeresin of a honed 48 hours Prior to testhllg- A 141 inch hole is Phnehedstyrene-divinyl benzene copolymer matrix containing a in the center ofthe sample with a Punch 0f the yp used quatinized base of dimethyl aminomethacrylate. 111- to prepare sheets for loose leaf binders. Thethickness of coway TM-l is marketed by the Illinois W te Tr tthe sampleis measured to the nearest 0.1 mil on each merit Company. In Example 2,the latex polymer is the side of the hole (along the 1 inch dimension ofthe sarnsame as that utilized in Example 1. In Example 3 the ple). Thefixture is clamped in the upper jaw of an Instron latex polymer is acopolymer containing 35% styrene, tensile tester. The bottom jaw of thetester is positioned 14% acrylonitrile, 50% butadiene and 1% acrylicacid. 0.15 inch below the bottom of the test fixtures. The two InExample 4 polyethyl acrylate is utilized and Example 5 ends of thesample are clamped in the lower jaw of the uses a plasticized vinylchloride marketed under the name Instron tester and the test run (at 10inches/min.) until of Geon 450X23 (Goodrich Chemical Company). In thesample tears. The maximum force developed in teareach example theproperties resulting from the deionized ing the sample is recorded. Theedge tearing resistance. is latex are compared to those of the samelatex without calculated by dividing the force recorded in grams by thesuch treatment. The properties for the products are given thickness ofthe sample on the side at which the sample in the following table:

Delamina- Elongation Fold Tear Example Tensile tion Resistance EnduranceStrength 2 Untreated 1,000 14 0.50 Deionized 1, 17 0. 55 3 Untreated...900 11 0.47 1,000 13 0. 45 720 20 0. 45 740 32 0. 03 1,100 19 0.37 1,20019 0. 42

When the impregnated papers prepared in accordance with the presentinvention are examined under the microscope the results aresubstantially the same as in Example 1. When the latex is removed fromthe product as in Example 1, it shows there is substantially nopenetration of the latex into the fibers of the paper just as in Example1.

EXAMPLE 6 The procedure of Example 4 is repeated employing a latexhaving a solids content of 60%. After deionization, however, the latexis concentrated to a solids content of 40%. After impregnating thesheet, the product has substantially the same properties as thatproduced in Example 4.

EXAMPLES 7-11 The first part of the procedure of Example 3 is repeatedusing 150 grams of water rather than 200 grams of water. The resultinglatex contains 40% by weight of synthetic polymer solids. In Example 7the resulting latex is diluted to 5% solids to give an uptake on thepaper of 6%. In Example 8 the resulting mixture is diluted to solids togive an uptake on the paper of 20%. In Example 9 the resulting mixtureis diluted to 20% solids to give an uptake on the paper of 40%. InExample 10 the resulting mixture is diluted to 30% solids to give anuptake on the paper of 60% and in Example 11 the resulting mixture 40%solids is used to give an uptake on the paper of 90%. The properties ofthe resulting impregnated paper are given in the following table.

What is claimed is:

1. A process for coating the surface of fibers of paper which comprises,applying a synthetic polymer latex containing from about 5% to about 70%synthetic polymer having over 95% of ions removed therefrom bycontacting with an organic cation/free base organic anion exchangedresin, thereafter applying the said latex to a cellulosic pulp paper,and drying the impregnated paper sufliciently so as to substantiallycoalesce the synthetic polymer on the surface of the fibers of the paperwhereby the interior of the fibers is substantially free of saidsynthetic polymer.

2. The process of claim 1 wherein the latex contains from about 15% toabout 50% synthetic polymer.

3. A fiber-coated paper which comprises a cellulosic pulp paperfiber-coated with at least 20%, based on the weight of the paper, ofcoalesced synthetic polymer latex solids having over 95% of ions removedtherefrom by contacting with an organic cation/ free base organic anionexchange resin, substantially all of the said latex solids beingcoalesced on the surface of the fibers of the paper whereby the interiorof the fibers is substantially free of said synthetic polymer.

4. The fiber-coated paper of claim 3 wherein the synthetic polymer latexsolids are present in an amount from about to about 100% based on theweight of the paper.

5. The fiber-coated paper of claim 3 wherein the synthetic polymer latexsolids are present in an amount from Delamina- Percent on Fold TearPolymer Tensile resistance endurance strength 0 004 0. 30 18 0.28 6 6760. 20 0. 27 20 73s 0. 5s 68 0.31 20 904 0. 130 0. 3s 40 909 0. 94 223 0.47 Deionoized 40 1022 1020 795 0. 45 10 Untreated 971 1.40 530 0. 57Deionized--- so 1240 1. 1968 0. 04 11 Untreated..- 1046 1. 93 412 0. 63Deionized 90 1200 2. 58 1422 0. 74

EMMPLE 12 about 40% to about 60% based on the weight of the In order toshow the advantages in electrical properpaper ties with the paperproduced in accordance with the pres- References Clted ent invention,the process of Example 3 is repeated em- 45 UNITED STATES PATENTSploying a crepe paper- Fo comparison Purposes, the 3,262,811 7/1966Sellet 117 X electrical reslstlvity is given for the paper, theuntreated 2,912,349 11/1959 Videen et a1 117 161 resin impregnated paperand the deionized resin ln'l- 2,912,350 11/1959 Videen et aL 117 161pregnated paper. The properties are given In the table 2,961,417 11/1960small below: 50 3,017,295 1/ 1962 Outterson et al 117-155 Electrical ,296/ 1962 Hatch 260-2.1 Percent resistivity 3,114,485 11/1963 Kunin 21038X polymer afia? 1%? 3,205,184 9/ 1965 Hatch 21038 X Latex Paper mpaper(A 595m; 3,300,416 1/1967 Hatch 260-21 0 12 55 3,303,155 2/1967 Petersonet a1. 117-155 X gfffz fiii aijj 40 2 3,332,890 7/1967 Hatch Deionized..d0---.- 40 26 3,335,100 8/1967 Geyer 117201 X While in the aboveexamples unmodified latex systems FOREIGN PATENTS are utilized, it isobvious that latex systems containing 1,131,013 6/ 1962 Germany.

anti-oxidants, fillers, pigments, oils, thickeners and the like can beemployed.

Many equivalent modifications will be apparent to those skilled in theart from a reading of the foregoing without a departure from theinventive concept.

WILLIAM D. MARTIN, Primary Examiner M. R. LUSIGNAN, Assistant Examiner

